Studies on the biosynthesis by uninfected chick embryo cells of gp85, the major glycoprotein of this avian tumor virus, have been carried out. The synthesis of gp85 that possesses type E specific antigenic determinants is detectable in uninfected chf plus but not chf minus cells. The expression of gp85 by chf plus cells is presumed to be related to the level of helper activity of these cells for the complementation of the defective Bryan high titer strain of Rous sarcoma virus. Since gp85 is a tumor associated antigen present in fetal cells, experiments will be undertaken to ascertain whether gp85 biosynthesis is detectable in cell cultures prepared from adult chickens. In addition to these experiments, a study of the synthesis by infected and uninfected chick embryo cells of gp37, the minor glycoprotein avian tumor virus will be undertaken. Experiments have also recently been initiated on the in vitro generation of cytotoxic chicken lymphocytes to cell surface antigens induced by Rous sarcoma virus.